Where is the Layers panel in Blender 2.8?
Blender 2.8 re-implements the scene layer system, as it had limitations. How it now works is explained here: Layers Manual and here: Blender Dev blog.

The scene layers are gone and their functionality was implemented in Collections (=groups) and View Layers.

Instead of sorting objects onto different scene layers, you can sort them into different Collections.


Add and Move between Collections with M
Link to Collection with Shift+M (so an object can be in multiple Collections)
Hide and Unhide Collections with CtrlH


Instead of using scene layers as masking layers in Render layers, now you can use Collections for masking or to effect only indirect rays (shadows and reflections):



View Layers are what you would call Render layers pre-2.8-Blender. Add them here:



A View Layer will remember your settings of objects and collections for visibility in view and render, selectability, holdout and indirect-only, etc. You find the settings for View Layers in the Properties panel: